The long-term goal of this proposal is to explore how the sarcolemma of cardiac cells links extracellular calcium to myocardial contractility, and to define how selected pharmacological interventions and pathological perturbations alter this linkage. The immediate specific aims of the proposal are as follows: (1) To obtain highly purified, selectively permeable sarcolemma vesicles from canine ventricular tissue with high yield; (2) to separate the vesicles into subpopulations consisting of right-side out (R/O) and inside out (I/O) vesicles; (3) to devise means by which the intravesicular and the extravesicular water space contents can be independently manipulated; and (4) to test three existing hypotheses that are concerned with pathways for calcium movement across the sarcolemma. These hypotheses concern the presence of a verapamil-sensitive calcium channel, an ATP-dependent calcium pump and a sodium-calcium exchange system. Techniques to be employed include various subcellular fractionation procedures, assays for enzyme activities and ligand binding and measurements of ligand fluxes.